In photography, a close-up filter, close-up lens or macro filter is a simple secondary lens used to enable macro photography without requiring a specialized primary lens.
Any lens has a minimal focal length. For instance with my 50mm I cannot focus on anything closer than about 60 cm. If I wanted to take a picture of anything closer I would have to buy special (expansive) lenses called macro lenses.
Close-up filters are a cheaper way. The results are not as great as with dedicated lenses but this way one can at least try some macro photography (and eventually later decide to buy a proper lens).
Today's pictures are just my first step towards the fascinating world of macro photography.
PS: I have no intention of starting to post macro pictures of insects. Even if I consider some of them very beautiful, that is just not my thing.